Hydrothelphusa A. Milne-Edwards, 1872

Cumberlidge, Neil & Sternberg, Richard V., 2002, The freshwater crabs of Madagascar (Crustacea, Decapoda, Potamoidea), Zoosystema 24 (1), pp. 41-79 : 47-51

Genus Hydrothelphusa A. Milne-Edwards, 1872

Hydrothelphusa A. Milne-Edwards, 1872: 2 ; 1887: 138. — Ortmann 1897: 299; 1903: 301. — Rathbun 1905: 266. — Balss 1929: 357. — Pretzmann 1961: 165. — Bott 1965: 339-340.

TYPE SPECIES. — Hydrothelphusa agilis A. Milne- Edwards, 1872, by original designation.

DISTRIBUTION. — Madagascar.

DIAGNOSIS. — Front distinctly indented. Anterolateral margin between exorbital, epibranchial teeth lacking intermediate tooth. Postorbital crests not meeting anterolateral margins. Mandibular palp twosegmented, bilobed, with medium-sized anterior process (about one-third size of terminal segment). Frontal margin widened in center forming triangular shape. Ischium of third maxilliped with deep vertical sulcus, exopod of third maxilliped with long flagellum. Thoracic sternal sulcus s2/s3 deep, horizontal, thoracic sternal sulcus s3/s4 deep, Y-shaped. Episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 not visible. Walking legs (p2-p5) normal length (neither shortened nor elongat- ed). Male abdomen long, slim, triangular. Terminal article of gonopod 1 short (ratio of length terminal article to subterminal segment 0.3); broad dorsal membrane at segment junction. Ventral side of subterminal segment of gonopod 1 with lateral flap folded inward, long, reaching to basal margin of segment; medial part of ventral face flat with distinct distomedial triangular shoulder, and large rounded basolateral projection; opening of chamber for gonopod 2 positioned about one-third of segment length from basal margin. Gonopod 2 longer than gonopod 1; terminal article of gonopod 2 long flagellum, ratio of length terminal article to subterminal segment c. 0.8.

REMARKS

Hydrothelphusa has been recognised as a distinct genus by every author ever since its original description in 1872. Bott (1955, 1960) assigned Hydrothelphusa to the subfamily Hydrothelphusinae in the then recognised family Potamonidae , and included two species, H. agilis and H. humbloti . Ng & Takeda (1994) assigned Hydrothelphusa to the Hydrothelphusinae which they included in the Potamonautidae , and these opinions are accepted here.

The present work recognises four species of Hydrothelphusa : H. agilis , H. madagascariensis , H. bombetokensis and H. goudoti n. comb. This represents a major departure from the concept of the genus by Bott (1965) which included only two species ( Table 1). In that work, H. agilis was recognised but H. madagascariensis was treated as a subspecies of H. agilis , H. bombetokensis was treated as a junior synonym of H. humbloti , and H. goudoti n. comb. was assigned to Gecarcinautes .

COMPARISONS

Hydrothelphusa can be distinguished from the five other genera of Madagascan freshwater crabs as follows: the bilobed terminal segment of the mandibular palp of Hydrothelphusa is similar to that seen in Malagasya n. gen. and Marojejy , however, the walking legs of Hydrothelphusa are of normal length, while those of Malagasya n. gen. and Marojejy are slender and elongated. In addition, the frontal margin of Hydrothelphusa is horizontal or slightly deflexed, whereas that of Malagasya is strongly deflexed, and the meri of the chelipeds of Hydrothelphusa and Malagasya are of normal length whereas those of Marojejy are elongated.

The bilobed terminal segment of the mandibular palp of Hydrothelphusa distinguishes this genus from Madagapotamon , Boreas n. gen. and Skelosophusa , where the terminal segment is either simple, or has a small hard ledge ( Skelosophusa and Boreas n. gen.). In addition, sternal suture s3/s 4 in adults of Hydrothelphusa is Y-shaped and completely crosses the sternum, whereas s3/s 4 in adults of Boreas n. gen. and Skelosophusa is incomplete, and consists only of two short notches in the sternal margins. Finally, the flagellum of the exopod of the third maxilliped is long in Hydrothelphusa , but virtually absent (a short stub) in Madagapotamon .

KEY TO THE SPECIES OF HYDROTHELPHUSA A. Milne-Edwards, 1872

1. Inferior margins of merus of p1 with either large teeth or large granules; anterior carapace texture rough, antero-lateral regions of carapace distinctly granular with short carinae ........................................................................................................ 2

— Inferior margins of merus of p1 either smooth or faintly granular; anterior carapace texture smooth, antero-lateral regions of carapace with faint carinae .................... 3

2. Frontal margin deeply indented, clearly toothed; front horizontal (not deflexed); suborbital margin with large pointed teeth; anterior margins of ischia of p1 and p2 with large pointed teeth ............................................................................ H. agilis

— Frontal margin shallowly indented, granular (not toothed); front moderately deflexed; suborbital margin granular; suborbital region of carapace sidewall granular; anterior margins of ischia of p1 and p2 smooth, lacking teeth .................. .................................................................................................. H. madagascariensis

3. Exorbital, epibranchial teeth both large, broad, outer margin of exorbital tooth long, clearly separating these teeth; epigastric, postorbital crests separated by distinct gap; cervical grooves very short; suborbital, pterygostomial regions of carapace sidewall both heavily granulated; carapace medium wide (cw/fw = 3.5), not highly arched (ch/fw = 1.3) .................................................................... H. bombetokensis

— Exorbital, epibranchial teeth both low, blunt; outer margin of exorbital tooth short and teeth close together; epigastric, postorbital crests fused forming long horizontal postfrontal crest; cervical grooves very long; suborbital, pterygostomial regions of carapace sidewall both smooth; carapace very wide (cw/fw = 3.9), highly arched (ch/fw = 1.6) .......................................................................................... H. goudoti

Hydrothelphusa agilis A. Milne-Edwards, 1872 ( Figs 1A ; 3A ; 4A ; 5A ; 6A ; 7A, B ; 8A ; 9 A-D; 11A)

Hydrothelphusa agilis A. Milne-Edwards, 1872: 2 . — Rathbun 1905: 266-268, fig. 72, pl. 15, fig. 7. — Balss 1929: 357. — Pretzmann 1961: 165. — Cumberlidge 1997: 584, 585.

Hydrothelphusa agilis agilis – Bott 1965: 340, 341, fig. 4, pl. 2, figs 8, 9, pl. 4, fig. 18.

TYPELOCALITY. — Madagascar, Sakaleone river.

MATERIAL EXAMINED. — Madagascar. Dry collection, coll. M. Grandidier, 1 ad. chosen as lectotype cw 50.2, cl 39.6 mm ( MNHN-B 4383 ) (see Rathbun 1904: 266 for more dimensions), 1 cw 46, cl 38.3 mm ( MNHN-B 27931 ) ; in alcohol, coll. Grandidier, 1 ad. paratype cw 60.9, cl 47.1 mm, 1 ad. paratype cw 54.5, cl 46.5 mm ( MNHN-B 5010 ) ; coll. M. Grandidier (exchange with Paris Museum), 1 subad. paratype cw 30.1, cl 24.2, ch 11.3, fw 11.1 mm ( NHM 1910.7.7.1). — Toamasina (formerly Tamatave), Autumn 1922, coll. J. Millot, 1 ad. ( MNHN-B 5009 ), 3 specimens ( MNHN-B 5011 ), 6 specimens ( MNHN-B 5013 ). — Andrafiavelo (Sakarava), 29.VIII.1930, coll. R. Decary, 1 juv. cw 21, cl 16.5 mm ( MNHN-B 5179 ). — Analamazastra river , Toamasina, Moramanga , 7.IX.1963, 1, 1 juv., 1 ad. cw 50.5, cl 42, ch 18, fw 16.5 mm, 1 subad. cw 41, cl 33.5, ch 13.5, fw 13 mm ( MNHN-B 25750 ) ; coll. J. Millot, Autumn 1922, 1 ( MNHN-B 15932 ). — Beforona, freshwater stream between Tananarive and Toamasina, 1897, coll. M. Bastard, 1 ad. ( MNHN- B 15933). — Analamazastra river, forest streams, 1926, coll. G. Petit, 1 ad., 1 ad. ( MNHN-B 15934 ), 2 subad. ( MNHN-B 15935 ). — Analamazastra river, Moramanga , collected in a net, IX.1958, 1 ad. ( MNHN-B 2625 ). — Ambodiriana ,

A B

road to Lakato, Moramanga, coll. Thérézieu, 3 subad. ( MNHN-B 25737). — Road to Toamasina, from lake near Mandrake dam, 28.V.1966, 1 ( MNHN-B 25738). — Ambodiriana, road to Lakato, Moramanga, 5.VIII.1960, coll. Thérézieu, 2 ad. ( MNHN-B 25748), 1 ad. ( MNHN-B 25749). — Analamazastra river, 1, 2 ad. cw 52, cl 43.5 mm and cw 49, cl 41.5 mm ( MNHN-B 26619).

DISTRIBUTION. — Madagascar ( Fig. 11A ). This species is found in the streams and rivers between Tananarive and Toamasina, in the region between Bombetok and Tananarive, and in the Sakaleone river near Mahela. See Cumberlidge (1998) for more localities. DIAGNOSIS. — Front horizontal (not deflexed); frontal margin deeply indented, toothed; exorbital, epibranchial teeth large, tips pointed; suborbital margin with pointed teeth. Ischium of p1 and p2 with two large teeth with pointed tips; inferior margins of merus of p1 with several long teeth with pointed tips.

REDESCRIPTION

Carapace moderately wide (cw/fw = 3.2) moderately high (ch/fw = 1.2); anterolateral, posterolateral carapace regions distinctly granular, with short carinae; rest of carapace surface rough. Epigastric crests rounded; mid-groove between epigastric crests broad; distinct gap between epigastric, postorbital crests; postorbital crests not meeting anterolateral margins. Semi-circular groove deep; urogastric, cardiac grooves shallow; cervical grooves long. Front horizontal (not deflexed); frontal margin toothed, deeply indented; frontal, posterior margins of carapace approximately one-third cw (0.3, 0.35). Exorbital, epibranchial teeth large, directed forward, tips pointed. Anterolateral margin posterior to epibranchial tooth raised, granular. Suborbital margin with pointed teeth, largest tooth at medial end. Anterior inferior margin of ischium of p1 and p2 with two large teeth with pointed tips, posterior inferior margin of pereiopod 1 with one pointed tooth. Inferior margins of merus of p1 with large teeth with pointed tips; distal margin with single pointed tooth; superior surface of merus roughly granulated. Inner margin of carpus of cheliped with two large, pointed carpal teeth; second tooth half size of first, margin behind second tooth smooth.

Size

The adult size range is from cw 45-50 to 76 mm. The carapace proportions are given in Table 3.

REMARKS

The unique features of H. agilis have long been recognised, and the assignment of this species to a distinct genus has never been seriously questioned. The undeflexed front, the deeply-indented toothed frontal margin, the toothed suborbital margin, and toothed p1 ischium are all characters peculiar to H. agilis .

Hydrothelphusa agilis can be further distinguished from the other three species in the genus as follows. The carapace of H. agilis is narrower (cw/fw = 3.2) than that of H. madagascariensis (cw/fw = 3.4) and the subhepatic and pterygostomial regions of the carapace sidewall of H. agilis are both smooth, whereas those of H. madagascariensis are heavily granulated. Hydrothelphusa agilis can be distinguished from H. bombetokensis by comparing carapace proportions — the carapace of H. agilis is less wide (cw/fw = 3.2) than that of H. bombetokensis (cw/fw = 3.5). In addition, the inferior margins of the merus of p1 of H. agilis have several large and pointed teeth, while these margins in H. bombetokensis are granular; and the anterior carapace of H. agilis is coarse, whereas that of H. bombetokensis is smooth. Hydrothelphusa agilis can be distinguished from H. goudoti n. comb. as follows: the carapace of H. agilis is less wide (cw/fw = 3.2) and less arched (ch/fw = 1.2) than that of H. goudoti n. comb. (cw/fw = 3.9, ch/fw = 1.6). The exorbital and the epibranchial teeth of H. agilis are both large with pointed tips, whereas these teeth in H. goudoti n. comb. are small and the tips are blunt; the inferior margins of the merus of p1 of H. agilis are lined by several large, pointed teeth, whereas these margins in H. goudoti n. comb. are granular; the anterior carapace of H. agilis is heavily granulated whereas that of H. goudoti n. comb. is smooth; and the second carpal tooth of the carpus of p1 is large with a pointed tip in H. agilis , and a low granule in H. goudoti n. comb.

The horizontal clearly indented and sharply toothed frontal margin of H. agilis are unusual characters in freshwater crabs in general, but are seen in African freshwater crab species such as the platythelphusid Platythelphusa armata A. Milne- Edwards, 1887, and the potamonautids Erimetopus brazzae A. Milne-Edwards, 1887 (particularly E. b. frontospinulosa Bott, 1955), and Potamonautes (Longipotamonautes) vandenbrandenii Balss, 1937 . However, this similarity is only superficial and may be convergent, for there is no other supporting morphological evidence linking any of these taxa (see Bott 1955; Cumberlidge 1999).

A detailed description of the arterial system of H. agilis was provided by Vuillemin (1964).

The present findings do not support Bott’s (1965) characterization of the terminal segment of the mandibular palp of H. agilis as “basally thickened”. In fact, this segment has a distinct bilobed terminal segment with a medium-sized anterior process. This point is important because H. agilis is the type species of the genus and subfamily, and so Bott’s (1965) genus and subfamily assignments are substantially challenged.

Hydrothelphusa madagascariensis

Figures

FIG. 1. — Dorsal view of the carapace of adult males of Madagascan freshwater crabs; A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb., holotype (FMNH 4651). Scale bar: A, 10.5 mm; B, 14.4 mm; C, 14.1 mm; D, 12.6 mm; E, 8.9 mm; F, 6.4 mm.

FIG. 3. — Inferior view of the sternum of adult males of Madagascan freshwater crabs; A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb., G, Madagapotamon humberti Bott, 1965; H, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; I, Boreas uglowi n. gen., n. sp. Scale bar: A, 11.7 mm; B, 17.2 mm; C, 15.9 mm; D, 14.5 mm; E, 10.2 mm; F, 7 mm; G, 9.6 mm; H, 6.4 mm; I, 9.1 mm.

FIG. 4. — Left mandible of Madagascan freshwater crabs, frontal view showing the palp (J, K based on Ng & Takeda 1994); A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2000) n. comb.; G, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2000; H, Boreas uglowi n. gen., n. sp.; I, Skeleosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Madagapotamon humberti Bott, 1965. Scale bar: A-I, K, L, 1.0 mm; J, 1.25 mm.

FIG. 5. — Left third maxilliped of Madagascan freshwater crabs, frontal view (J, K based on Ng & Takeda 1994); A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb.; G, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; H, Madagapotamon humberti Bott, 1965; I, Skelosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Boreas uglowi n. gen., n. sp. Scale bar: A-D, 5.0 mm; E-L, 3.5 mm.

FIG. 6. — Superior view of the carpus of the cheliped (pereiopod 1) of adult males of Madagascan freshwater crabs (J, K based on Ng & Takeda 1994); A Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Malagasya antongilensis (Rathbun, 1905) n. comb.; F, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb.; G, Madagapotamon humberti Bott, 1965; H, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; I, Skeleosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Boreas uglowi n. gen., n. sp. Scale bar: A-D, 5.5 mm; E-L, 3.5 mm.

FIG. 7. — Superior and inferior views of the merus of the cheliped (pereiopod 1) of adult males of Madagascan freshwater crabs; A, B, Hydrothelphusa agilis A. Milne-Edwards, 1872; C, D, H. madagascariensis (A. Milne-Edwards, 1872); E, F, H. bombetokensis (Rathbun, 1904); G, H, H. goudoti (H. Milne Edwards, 1853) n. comb.; I, J, Malagasya antongilensis (Rathbun, 1905) n. comb.; K, L, Madagapotamon humberti Bott, 1965; M, N, Skelosophusa gollhardi (Bott, 1965); O, P, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; Q, R, Boreas uglowi n. gen., n. sp. Scale bar: A-H, 5.0 mm; I-T, 3.0 mm.

FIG. 8. — Last walking leg (pereiopod 5) of adult males of Madagascan freshwater crabs (H based on Ng & Takeda 1994); A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853) n. comb.; E, Boreas uglowi n. gen., n. sp.; F, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; G, Madagapotamon humberti Bott, 1965; H, Skelosophusa prolixa Ng & Takeda, 1994; I, Malagasya antongilensis (Rathbun, 1905) n. comb.; J, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb. Scale bar: A-D, 5.0 mm; E-L, 2.6 mm.

FIG. 9. — Right first gonopod (dorsal view; superior view; ventral view) and right second gonopod (dorsal view) of adult males of species of Hydrothelphusa A. Milne-Edwards, 1872; A-D, H. agilis A. Milne-Edwards, 1872; E-I, H. madagascariensis (A. Milne- Edwards, 1872); J-M, H. bombetokensis (Rathbun, 1904); N-Q, H. goudoti (H. Milne Edwards, 1853) n. comb. Scale bar: 4.5 mm.

FIG. 11. — Summaries of the known distribution of the Madagascan freshwater crabs; A, Hydrothelphusa agilis A. Milne-Edwards, 1872; B, H. madagascariensis (A. Milne-Edwards, 1872); C, H. bombetokensis (Rathbun, 1904); D, H. goudoti (H. Milne Edwards, 1853); E, Marojejy longimerus Cumberlidge, Boyko & Harvey, 2002; F, Malagasya antongilensis (Rathbun, 1905) n. comb.; G, M. goodmani (Cumberlidge, Boyko & Harvey, 2002) n. comb.; H, Madagapotamon humberti Bott, 1965; I, Skelosophusa gollhardi (Bott, 1965); J, S. prolixa Ng & Takeda, 1994; K, S. eumeces Ng & Takeda, 1994; L, Boreas uglowi n. gen., n. sp.